For example, an absorbent article including a web having long crimped fibers oriented in one direction and having a highly-absorbent polymer embedded and carried therein has been known as a sheet excellent in diffusion of a liquid and absorption thereof in the inside (see Japanese Patent No. 3871698 (PTD 1)). In order to realize diffusibility and absorptiveness, however, the absorbent article disclosed in PTD 1 achieves the function with an extremely complicated structure based on combination of materials different in form such as calamus long in fiber, a highly-absorbent polymer, and tissue paper or based on requirement for a stack structure of materials and structures different from one another.
A waste ink absorber having a diffusion layer formed from fiber sheets which contain fibers having a standard moisture regain lower than 5% at least on one side of a liquid retaining layer which contains fibers having a standard moisture regain not lower than 5% and is formed from entangled fiber sheets has been known (see Japanese Patent No. 3621567 (PTD 2)). In order to maintain a form of the fiber sheet forming the diffusion layer, however, the waste ink absorber disclosed in PTD 2 achieves that function by employing a thermally fusible fiber component which is not directly relevant to a diffusion and absorption function or by employing a complicated layered structure for that function.
Japanese Patent Laying-Open No. 2010-222717 (PTD 3) discloses a method of manufacturing nanofibers by fibrillating fibers in a direction of length by applying cavitation energy to a fiber assembly and at least partially converting the fibers forming the fiber assembly into nanofibers. According to the background art in PTD 3, in connection with “fibrils”, “A crack is produced in parallel to the direction of length of fibers by applying impact force in a direction of a diameter of fibers (except for glass fibers or metal fibers). A phenomenon that a crack is produced in a fiber and the fiber is split into finer fibers is called fibrillation, and the split fibers are called fibrils (fine fibers). The fibril is considered to be formed as an assembly of microfibrils which are finest fibers specific to each fiber material.”
For example, Japanese Patent Laying-Open No. 2009-132055 (PTD 4) discloses as a technique using such fibrils, a friction material for a car which is derived from a single-layer fabric containing liquid crystal high-polymer fibers and has more fibrils in a surface layer portion on a side of a friction surface than in a surface layer portion on a side of the other surface.